1. Field of the Invention
The present invention is generally concerned with centering an ophthalmic lens relative to a reference axis and the operations usually accompanying such centering.
2. Description of the Prior Art
As is well known, in order to match an ophthalmic lens to the specific contour of the rim or surround of the eyeglass frame to which it is to be fitted, it is usually ground on a grinding machine and, in order to fit it to and support it on the grinding machine, it is usual to apply to it a handling and support block, such as a simple sucker, for example, adapted to adhere to it in a removable way.
When the ophthalmic lens is a prescription lens, it is important that its position relative to the rim or surround of the eyeglass frame to whic it is to be fitted, and therefore its preliminary grinding to suit the contour of the latter, shoudl take into account various ocular parameters, in particular the interpupillary distance of the person concerned.
It is therefore important that, before it is fitted to the grinding machine used to grind it, its optical center is very strictly located relative to a reference axis, which may simply be that of the handling and support block to be applied to it, for example.
However, it is also necessary to ensure that the rim or surround and the ophthalmic lens to be fitted to it are compatible, by comparison of the lens with a template representing the rim or surround of the eyeglass frame, since grinding of the lens should not lead to removal of any substantial part of its operative sight correcting part.
Centering devices which make provision for such comparison have already been proposed.
This is the case, for example, with that which is the subject matter of French patent application No. 72 19694 of June 1, 1972 published under the number 2 188 182.
To the stated end this centering device comprises, on a frame, a translucent first support plate adapted to receive an ophthalmic lens to be centerd, a frosted screen at the base of said first support plate, a projector system above said first support plate adapted to project an image of said ophthalmic lens onto said frosted screen, a first observation channel and an opening in said frame enabling an operator to view said frosted screen, a second support plate adapted to receive a template with which said ophthalmic lens is to be compared, and a second observation channel adapted in conjuction with said opening in said frame to enable said operator to view said second support plate, said first and second observation channels sharing a common emergent section of which said opening forms part.
Thus the operator can view at the same time the superposed images of the ophthalmic lens to be ground and of the template corresponding to the rim or surround of the eyeglass frame to which it is to be fitted. After centering the ophthalmic lens relative to the corresponding reference axis, the operator can then check that the compatibiity between it and the rim or surround of the eyeglass frame is actually satisfactory.
However, in the centering device in question the support plate adapted to receive a template is in practise at the rear of the frame of the device and consists in a drawer sliding laterally relative to the frame.
This has various disadvantages.
First of all, and by virtue of its position at the back of the frame, the accessibility of the support plate implemented in this way as a drawer is relatively mediocre, which makes the operations needed to fit a template to it somewhat difficult.
Also, there is more than one operation involved, namely extracting the drawer from the frame, fitting the template to the drawer and reinserting the combination into the farme, which inevitably wastes a significant amount of operator time.
Finally, and most importantly, the returning of the drawer consitutes the template support plate to its initial position is not adequately controlled, so that there remains some uncertainty as to the position of the drawer and thus of the template in the device when the ophthalmic lens to be ground is compared with the template.
A general object of the present invention is an arrangement providing a very simple way of circumventing these disadvantages.